Molecular analyses are frequently used to assess biological gene flow and dispersal, yet recent data suggest that the operation of density-dependent priority effects often leads to underestimation of species movement patterns and associated invasive potential. Although individual movement is broadly considered to promote connectivity among populations, emerging genetic evidence on a range of scales indicates that it often fails to do so; instead, it can be a strategy that allows first colonizers to wedge a ‘foot in the door’ when new space becomes available. Founding lineages can then rapidly dominate, blocking colonization by later arrivals; subsequent invasion opportunities may be contingent on the extirpation of locals. Many contemporary studies, however, ignore the role of such density-dependent priority effects, and thus fail to assess major differences between movement and establishment. Understanding the role of these processes in the successful establishment of dispersing organisms is critical if we are to predict distributional range shifts and deal with invasive pest species.